Crimpable copolyamide filaments

ABSTRACT

Filaments which develop crimp when relaxed, of a copolymer composition comprising 6-12 nylon polymer units and N-substituted 6-12 nylon polymer units wherein the N-substituent is an alkyl group of 2 to 4 carbon atoms, from 15 to 50 percent of the nitrogen atoms in the copolymer being alkyl substituted. The filaments are particularly suitable for use in stretch hosiery. They provide a much softer feel and much lower snagging propensity than conventional stretch hose of 66 nylon, while avoiding undesirable characteristics of elastomeric filaments.

n ite States Patent 1 Ulsnim 451 Dec. 18, 1973 CRIMPABLE COPOLYAMIDE FILAMENTS [75] Inventor: Earl Herbert Olson, Wilmington,

Del.

[22] Filed: Jan. 5, 1972 [21] Appl. No.: 215,683

[52] US. Cl 161/173, 161/172, 161/70,

260/78 R, 260/857 TW, 66/178 A [51] Int. Cl D02g 3/00, C08g 20/00 [58] Field of Search 161/172, 173, 175, 161/177; 260/857 TW, 78

[56] References Cited UNITED STATES PATENTS 3,667,207 6/1972 Ben et a1 l6l/l73 X 3,485,805 12/1969 Cowell et al 260/857 Schickh et a1. 260/78 Anton et al 161/175 Primary ExaminerGeorge F. Lesmes Assistant Examiner-P. Thibodeau Att0rneyN0rris E. Ruckman 5 7] ABSTRACT Filaments which develop crimp when relaxed, of a copolymer composition comprising 6-12 nylon polymer units and N-substituted 6-12 nylon polymer units wherein the N-substituent is an alkyl group of 2 to 4 carbon atoms, from 15 to 50 percent of the nitrogen atoms in the copolymer being alkyl substituted. The filaments are particularly suitable for use in stretch hosiery. They provide a much softer feel and much lower snagging propensity than conventional stretch hose of 66 nylon, while avoiding undesirable characteristics of elastomeric filaments.

3 Claims, N0 Drawings CRIMPABLE COPOLYAMIDE FILAMENTS BACKGROUND OF THE INVENTION This invention relates to improved polyamide filaments which are particularly suited for use in stretch hosiery.

Synthetic polyamide filaments and yarns have been predominant in the womens hosiery market for many years. In this market there is now an increasing demand for the so-called stretch hose. Hose of this type are much smaller than conventional hose but have the abil-- ity to stretch much more and thereby have improved fit as well as reducing the number of sizes of hose required to fit the range of leg sizes normally encountered.

Filaments of elastomeric polymers have been tried in hose but were found undesirable because of their cold, limp, rubbery feel. A more successful approach to stretch hose has been found in the use of nylon filaments which develop a helical crimp in a relaxed state either spontaneously or on application of heat. Composite filaments which behave in this fashion are described by Olson in U.S. Pat. No.'3,399,l08. Other filaments of this type may be prepared by various twisting or false-twisting techniques which are well known in the art for preparation of stretch yarns. These filaments tend to distort the stitches in the hose as they attempt to crimp and thus produce hose which are capable of stretching more than hose made from non-stretch yarn. Although these filaments have produced good stretch hose, further improvements are desirable.

SUMMARY OF THE INVENTION I filaments which are self-crimpable in that they develop crimp when relaxed. The copolymer consists essentially of 6-12 nylon polymer units and N-substitute'd 6-12 nylon polymer units wherein the N-substituent is an alkyl group of 2 to 4 carbon atoms, e.g., ethyl, n-propyl,

isopropyLn-butyl and isobutyl. From 15 to percent of the nitrogen atoms in the copolymer are alkylsubstituted. The copolymer can be prepared from hexamethylen'ediamine, N,N '-dialkylhexamethylenediamine and dodecanedioic acid. The copolymer may be a random copolymer or a block copolymer. Self-crimpable filaments for the purposes of this invention are filaments which have the characteristie that they develop substantial crimp when relaxed Although straight, uncrimped filaments of the above composition are unsatisfactory in hosiery due to the limp, rubbery feel of the hose, it has been found, surprisingly, that the crimpable filaments of this invention yield hose with a soft, non-rubbery feel, a snug fit without the sliding on the leg commonly found in prior art hose, and a low propensity for snagging and developing runs.

The crimping of the filaments is preferably carried out by false-twist crimping techniques known in the art, one such method being illustrated subsequently. Other procedures falling generally in the category of torque twisting or torsional stressing of the filaments may be employed, e.g., procedures described by Mark G. l-larrison in Textured and Novelty Yarn Processes, Chapter 2, page 103, Noyes Development Corporation, Park Ridge, NJ. (1967).

The filaments of this invention may contain any of the various additives commonly employed in the production of filaments, such as delusterants, pigments, dyes, anti-oxidants, antistatic agents and surface modifying agents. Yarn of different deniers and filament count, e.g., 15, 20, and 30 denier monofils; 20 denier, 3 filament; 40 denier, 6 filament, etc., may of course be prepared.

The expression relative viscosity as used herein signifies the natural logarithm of the ratio of flow time in a viscometer of a polymer solution containing approximately 0.5 percent by weight of polymer, relative to the flow time of the solvent by itself, divided by the concentration. Measurements of relative viscosity are made with 0.25 gram of polyamide in 50 milliliters of metacresol at 25C.

The strength of the filaments or yarns is usually expressed in terms of tenacity and may be measured by conventional means. Values given herein were measured on yarn conditioned at 25C. and 65% RH using an Instron tester. The tenacity after boil-off is measured on yarn which has been boiled in water for 30 minutes under no load, dried at 25C. and conditioned as above. The tenacity of a conventional yarn is calculated on a basis of the denier of the yarn as measured before testing. However, since the yarn of this invention elongates considerably before breaking, the actual denier at the breaking point is substantially lower than the initial denier. Therefore, tenacity based on the breaking denier is a more useful value for comparing different fibers. Tenacity in grams per denier at break (T may be calculated from the usual tenacity value (T) and the percent elongation at the breaking point (E) as follows: T T(l E/l00).

Initial modulus is indicative of the rate at which yarn elongates with increasing load in the early stages of elongation. Practically, it is determined from the stressstrain curve (obtained when the boiled off yarn is elongated 2 percent in an lnstron tester) by multiplying the load at 1 percent elongation by and dividing by the denier of the yarn.

Set twist is a measure of the useful twist which has been heat set in a false-twist textured filament or yarn. A sample is allowed to relax and twist under a load of 1.2 mg. per denier and is exposed to a gentle flow of atmospheric steam until no further twisting occurs. Details of the test procedure are described in Dugas U.S. Pat. No. 3,608,299.

As illustrated in the following examples, the copolymer filaments of this invention may readily be given a set twist of at least 40 turns per inch. Preferably, they are characterized by a tenacity of at least 5 grams per denier at break, an elongation at break of at least 100 percent'and an initial modulus of less than 4 grams per denier measured after relaxed boil-off.

EXAMPLES The salt of N,N'-diethylhexamethylenediamine and dodecanedioic acid is prepared as follows: 5,000 g. of N,N-diethylhexamethylenediamine are added to 4.3 liters of isopropyl alcohol. The diamine solution is added with stirring to a 5060C. solution of 6,510 gm. of dodecanedioic acid in 44 liters of isopropyl alcohol,

the solution being kept under a nitrogen atmosphere. The warm solution is stirred until a clear solution is obtained. Forty-four liters of isopropyl alcohol are then added to the mixture which is cooled to -l0C. to precipitate the salt. 1f the salt fails to precipitate on cooling, 2 gallons (7.6 liters) of ethylacetate are added to bring about precipitation. The salt is then filtered off and dried at 50C. for 24 hours. The salt plus 0.6 percent by weight of formic acid, 0.2 percent boric acid, 2 percent N,N-diethylhexamethylenediamine, 0.03 percent potassium phenylphosphinate, and 6 percent water are heated in a closed autoclave with agitation to a temperature of 215C. over a period of 270 minutes. The pressure in the autoclave is then reduced to atmospheric and the temperature increased to 295C. over a period of 90 minutes. This temperature is maintained for 30 minutes while the autoclave is flushed with dry nitrogen. While maintaining this temperature, the pressure in the autoclave is then reduced to 10 millimeters of mercury and maintained at this level for 240 minutes. The resulting poly(N,N-diethylhexamethylenedodecanedioamide) is cooled to 250C., extruded and dried in a vacuum oven at 120C. for 24 hours. The final N-substituted 6-12 nylon polymer has an inherent viscosity of 1.3.

A 6-12 nylon polymer is prepared from the salt of hexamethylenediamine and dodecanedioic acid in the conventional manner, cut into flake and dried. The resulting poly( hexamethylenedodecanedioamide) has an inherent viscosity of 1.28.

The two polymers prepared as above are mixed, in proportions of 50 percent, 60 percent and 70 percent of the 6-12 nylon polymer and 50 percent, 40 percent and 30 percent by weight of the N-substituted 6-12 nylon polymer, in a homogenizer at 300C. to form block copolymers and then pumped to a conventional spinneret assembly. The total elapsed time from mixing to extrusion of the resulting copolymer is 40 minutes. Analysis of the copolymer indicates about 10 percent of amide interchange between the two polymers. Block copolymers containing 50 percent, 60 percent and 70 percent by weight, respectively, of 6-12 nylon polymer units, prepared in this manner are extruded to form monofilaments which are quenched in air at 25C. The filaments are then given 5 passes around a feed roll operating at 330 yds./min. (302 meters/min.) peripheral speed, and its associated separator roll, and then 11 passes around a draw roll having a peripheral speed of 1,300 yds./min. (1189 meters/min.) and its associated separator roll. The filaments are then passed to another roll operating at 1,300 yds./min. and then to a roll operating at 1,250 yds./min. (1,143 meters/min), and finally wound into a package in the conventional manner at 1,200 yds./min. (1,097 meters/min). Subsequently, the filaments are withdrawn from the package and given an additional 1.4X draw in order to reduce the elongation to the desired range of 30 to 33 percent. The drawn filaments are of denier.

The filaments are then processed with an apparatus of the type disclosed in Dugas U.S. Pat. No. 3,608,299, but without the coupled drawing step, i.e., the draw roll is used as a feed roll. The filament is fed at 420 yards per minute (384 meters/min.) to the jet device used for heating the filament. Hot air is supplied to the jet device at 200-220C. during start-up, and the temperature is increased to 260C. at the inlet for normal operation, the outlet air temperature being 178C. The heated filament then passes through the torque jet device, supplied with cool air, which is operated to generate a set twist in the filament amounting to 40-57 turns per inch when the packaged filament is tested as described previously. From the torque jet, the heat-set filament passes over the take-up roll and is packaged. A reduced take-up speed, relative to the feed roll speed, is used to provide 18-20 percent filament retraction for filaments containing 50 percent and 60 percent 6-12 nylon polymer units, and 14-18 percent filament retraction for filaments containing percent 6-12 nylon polymer units.

Packages of filaments having S twist and other packages having Z twist are prepared as above. The S and Z twist yarns are then fed in pairs to a double feed knitting machine where they are knit into stretch hose. After knitting, the hose are boiled off in a relaxed state to develop the crimp and to shrink the hose to approximately finished dimensions. The hose are then preboarded by placing the wet hose on a board and subjecting them to 107C. steam for 2 minutes followed by 107C. dry heat for 2 minutes. Properties of filaments removed from the hose after finishing in this manner are shown in Table 1 below. For comparison, similar properties are shown for a false-twist, textured yarn prepared from 15 denier 66 nylon as described in Example Xlll of the Dugas patent.

TABLE 1 false Twist 6-12 polymer units, wt. 50 60 70 66 Nylon Tenacity, T gpd 5.77 6.07 5.73 6.02 Elongation at break, 125.6 131.7 100.7 55.6 Initial modulus, gpd 1.5 1.8 3.5 7.7

As can be seen from the above table, the tenacity at the breaking denier is substantially equivalent to that of 66 nylon while the initial modulus, which leads to a much softer feeling hose, is much lower. Surprisingly, the lower modulus does not produce a limp, rubbery feel in the hose. On the contrary, the hose has a soft, warm feel, a snug fit with no slipping on the leg and the snagging propensity is much less than for the stretch hose from 66 nylon.

1 claim:

1. Copolymer filaments which develop crimp when relaxed, the copolymer consisting essentially of hexamethylenedodecanedioamide polymer units and N- substituted hexamethylenedodecanedioamide polymer units wherein the N-substituent is an alkyl group of 2 to 4 carbon atoms, from 15 to 50 percent of the nitrogen atoms in the copolymer being alkyl-substituted said filaments being characterized by a tenacity of at least 5 grams per denier at break, an elongation at break of to 132 percent and an initial modulus of 1.5 to 4 grams per denier measured after relaxed boil-off.

2. Copolymer filaments as defined in claim 1 characterized by a set twist of at least 40 turns per inch.

3. Copolymer filaments as defined in claim 1 composed essentially of a block copolymer of 50 to 70 percent poly(hexamethylenedodecanedioamide) and 30 to 50 percent poly(N,N'-diethylhexamethylenedodecanedioamide 

2. Copolymer filaments as defined in claim 1 characterized by a set twist of at least 40 turns per inch.
 3. Copolymer filaments as defined in claim 1 composed essentially of a block copolymer of 50 to 70 percent poly(hexamethylenedodecanedioamide) and 30 to 50 percent poly(N, N''-diethylhexamethylenedodecanedioamide). 